what problems do people run into with running a larger cam with EFI?

(my specs are in the slixers gallery, under "sick 6's duster")

I'd tend to think that bigger cams are a piece of cake with efi since you don't depend on manifold vacuum for the correct metering of the fuel (as stated previously and correctly by dan) what is wrong with big cams and efi, lucky13? maybe I'm reasoning carburetingly...

And after years and years of carefully tailoring carbs, I can tell you that more than 90% of the carbureted cars I've seen has problems. All of them are dumping excessive amount of fuel at idle, and the emulsion stages are sometimes clogged, they always jetted too rich, and the power valve gives little enrichment so when you really step on it sucks. out of 100% of factory EFI cars, I'd say that the chance of them going wrong is pretty much the sensors, and/or the computer going mad, wich are only few cases, so it's really more effective but because people tends to miscomprehend the carburetors. It's like FWD... it ain't safer than RWD (the only conceivable wheel drive for me, driving a FWD is a pain in the but to me) just cuts on power transmitted to the ground.

Tailoring a carb for a specific engine is like going aftermarket EFI setup. A pain in the ass... And you don't have expect a 5 emulsion stages modified metering block from a simple device like a 2300 500 cfm to perform "decent" on all engines but "excellent" in the one you're aiming for. If other engine shares some particular configuration with it, well let's call you lucky!

That said, I think that the most you expect outta the car, you gonna get it by carefully tuning. I prefer to use taps, lathes, custom air bleeds and circuit enlargement, others prefer to use VOHM multitesters, splicers, cutters, wiring, soldering, etc.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Speed density EFI systems determine engine load by looking at....

Manifold vacuum.

Big cams will mess up a speed density EFi system and can mess up a MAF EFI system. I could go into detail why but it's late and I don't feel like it.

Steve

argentina-slantsixer and others;

Since you are expert on carbs,

This took me long time to find info online generally about carb operations. Do you have books to recommand on these to understand carb operation better? If books have ISBN numbers that would be awesome.

recently bought weber 32/36 for my 2.2, have to install correct linkage, etc, and was set up for air cooled 1700cc VW.

While I'm still running two barrel holley 5220 on caravan's 2.2, and is running great with poor 13 MPG I wanted to figure out and fix that for 19MPG or so.

I'm aware of the six jets and emulsion tubes in that 5220. Four is replaceable jets, while other two jets are for idle which are pressed into top carb half itself. When I rebuilt carb, I did not find anything that is clogged. (Stumped) Oh, choke does open up as it should.

Is there failure modes that can could cause MPG to plumment, don't exclude the engine issues even it's running "nicely"?

I'm curious.

Cheers, Wizard

hey wizard... not sure I'm a carb expert, much more like a carb messer extraordinaire, but never had the experience of playing (fiddling, destroying) a 5220. I'm going online to find some material on it and would sure get back to you as soon as I can understand how does it work. I know they're webber derivatives so it shouldn't be hard to figure out... but gimme some time.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Wow argentina-slantsixer.

Anyway, cool. Share your thoughts anyway. I'll look for books. I've just sent a PM to Dave at allpar about putting up a article on carb.

The holley & 32/36 Weber shares similar idea, basic idea was they have six jets, staged two barrel, progressive or vacuum secondary.

pair of main jets and air jets, two emulsion tubes and two idle jets (weber's are replaceable, holley copycats tiny jets are pressed into upper halve).

Cheers, Wizard

OK try'n enlarge the air jets. They're stamped. Tell me what you have now and I can make a more accurate suggestion. Other thing to look at, is that webbers and some solex have a very intrincated double spring loaded power enrichment circuit that uses a diaphragm... is like a "protruding triangular nose" that sticks out from the fuel bowl, pointing forward. Do you have that? time to check up on its function now. Get a Liesle vac pump and see if it's working. Pressed idle jets are a bitch... you just can't play with them... And playing with them affects not only idle but the early stage of "off-the-line" thing. Is you stomp it, how does it feels?

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

PS: A413 is like your A904 (3 speed with throttle valve cable).

No bogs, just take forever to accelerate and no kickdown before 1/2 throttle. I can make a good acceleration (headstart) by pressing the pedal suddenly to take off at standstill.
Have to stomp on gas to force trans to kickdown to tap into power in upper rpms.

Two items I have not looked at yet is is keep turning the idle screw in (had turned it 1/4 in when I rebuilt it last fall). Secondly, haven't looked at camshaft centerline to see if was retarded. I've got the kit except make a solid lifter.

The holley 5220 uses press in idle air jets in upper halve (air horn) and have power valve (replaced diaphgram and tested it). How loose is the power valve plunger assembly is? This one in the fuel bowl.

Cheers, Wizard